I can’t speak to the very specific thought process I had at the time, but it was probably not included in the data set I used. There are literally thousands of streams in the area, and there’s not room to fit them all, so I had to make some decisions on which were the most significant in length. In this case, I used a data set from the federal government which eliminated the smaller features to make those decisions.

Thanks for the kind words. Though locally significant, the Anacostia is a pretty short river. The label for “Washington,” for example, is bigger than the entire river’s length on a map like this. It would seem out of place, I think, to include something that small at this scale, especially while leaving off the hundreds of rivers longer than the Anacostia.

As to the Potomac, I thought for a time about how to treat the various branches, which all have lengthy official names such as “North Fork South Branch Potomac River.” Through the series, I decided to just keep the labeling scheme fairly minimalistic as a style decision (and a space decision), by stripping all those sorts of qualifiers and just retaining the base name.